1. Field of the Invention
The invention relates to a flexible double U-joint which is particularly adapted for use in the in-line inspection of pipelines.
2. Description of the Prior Art
With oil and gas line installations, it is customary both incident to the on-site construction thereof and periodically during the life of the pipeline to conduct an internal inspection to determine the extent of corrosion or damage. For this purpose devices such as TV cameras and ultrasonic inspection devices, along with other inspection equipment well known in the art, are inserted into the pipeline and moved along the length thereof to achieve the desired inspection.
Incident to these inspection operations, the pipeline inspection device must be inserted into the pipeline by moving it into a pipe somewhat larger in inside diameter than the outside diameter of the inspection device. It is customary to force the device into the pipeline by pushing it from the rear. Customarily, these inspection devices consist of from three to eight sections connected together by universal joints to allow the device to negotiate bends in the pipeline. To negotiate very sharp bends, simple universal joints are replaced by double U-joints. Although single U-joints are semirigid and thus can be pushed without buckling or bending in a pipeline, double U-joints, on the other hand, have no rigidity and thus cannot be pushed into the pipeline. Consequently, it is necessary to pull these devices into the pipeline. This is difficult to accomplish as the means for connecting the device to the arrangement exterior of the pipe to achieve this pulling action is cumbersome, since it is required that the connection extend through a reclosable opening a short distance downstream from the entrance opening to permit the required pulling action.